mineral

Quartz (Chert/Chalcedony variety)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: tan, cream, or light grey with a waxy/vitreous luster; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: approx. 2.65.

Hardness: 7 on Mohs scale
Color: tan, cream, or light grey with a waxy/vitreous luster

Identified April 8, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids in sedimentary environments. Common in marine deposits and as nodules in limestone or chalk.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include abrasives, semi-precious gemstones/cabochons, and as an additive in concrete.

Geological facts

This specimen appears to be a water-worn river stone or a weathered nodule. Chert is so hard it can create sparks when struck against steel, a property used by ancient humans to start fires.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), waxy feel, and smooth curved (conchoidal) breaks. Found globally in riverbeds and sedimentary rock outcrops.

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